I had hoped to find out the answer to your question when I first started researching pellet stoves. But, I eventually learned there is no "buy this stove, it works the best" answer. There are a few well known brands that are pretty well respected by most. In my exhaustive research I kept coming back to 3 stoves of which I have already mentioned....Enviro M55, Harman Accentra, and Quadrafire Mt. Vernon.
The Enviro and Mt Vernon are the quietest and have the highest BTU input. The Accentra is a bottom feeder which is nice because you don't hear the "plink, plink" as the pellets fall down the chute. However it's fans are noisier than the other two. The Mt Vernon has a (in my opinion) rinky dink automatic dump of the burn pot that I personally don't feel is engineered very well. It shuts down every 2hrs or so to dump, then restarts. Some don't mind, but I also hear others complain when they are in the dead of winter trying to keep the house warm and the stove is shutting down. Also, it doesn't slide out on rails which is an extremely important detail in my opinion for an insert. Also, some complain that it doesn't always dump the clinker as it will stick to the sides of the burn pot. These stoves are heavy and I can't imagine trying to slide mine out without a rail system like the M55 and Accentra have. The Enviro has a nifty burn pot with an agitator that keeps the burn pot free of clinkers and moves the ashes into the ash bin. I have had trouble with a noisy auger motor and squealing convection blowers. Enviro has been good to deal with on the warranty parts. I installed the parts myself as it's very easy. However the Accentra has a better thought out rail system that incorporates the exhaust as well as the OAK. Enviro seems to have forgot about the OAK in their rail system and unless you are mounting your stove by an outside wall, figuring out how to make the oak connection is a pain.
I could go on further, but I think you get the idea. Each one has it's pros and cons. Keep researching and learn as much about each stove as you can. Then decide what matters the most to you and go for it.
Flynfrfun